1. Field of the Invention
The present invention relates to an integrated coal gasification combined cycle system plant.
This application is based on Japanese Patent Application No. 2004-188888, the content of which is incorporated herein by reference.
2. Description of Related Art
In a heretofore known integrated coal gasification combined cycle system (hereinafter referred as “IGCC” in some cases), coal as a solid fuel is converted into a gas by a coal gasifier and is then used for a gas turbine combined power generation system. The IGCC has the following advantages. For example, coal resources, which have abundant reserves, are used; compared to a conventional thermal power generation using pulverized coal, the thermal efficiency is high and the amount of emitted air pollutants such as CO2 is small; and since ash is discharged in the form of glassy molten slag, the volume of the ash is decreased. Accordingly, the IGCC was developed as a main technology for future coal fired power generation.
The gas obtained by coal gasification using a coal gasifier contains sulfur components (such as H2S and COS), and hence in the IGCC, a system for removing the sulfur components is provided. In an IGCC of the related art, the sulfur components are removed by a cold gas clean-up system before the gas is combusted in a gas turbine.
However, in the cold gas clean-up, moisture and CO2 contained in the syngas are partly removed, and in addition, the syngas is cooled in this step. Hence, there have been problems in that the thermal loss is increased and the power generation efficiency of the IGCC system is degraded. In addition, since the gas clean-up is performed under high-pressure conditions, the number of equipment of the gas clean-up system is increased. As a result, the clean-up system becomes complicated, and costs for maintenance and the like are increased, thus the economical efficiency is deteriorated. Furthermore, the sulfur components remaining in a gas turbine exhaust gas are partly made to react with ammonia supplied in a selective catalytic reduction (SCR) system to form ammonium sulfate particulate dust, and subsequently the dust is discharged without being removed, which is undesirable.
Accordingly, in order to overcome or avoid the above problems, an IGCC plant in which a system for removing sulfur components is disposed at an exhaust side of a gas turbine has been proposed (for example, see Japanese Patent No. 2733188 (pp. 3 to 4, FIG. 1 etc.) and Japanese Patent No. 2954972 (pp. 5 to 6, FIG. 1 etc.)).
In the IGCC plant disclosed in the above Japanese Patent No. 2733188, uncombusted char in the syngas is removed by a high-temperature dust removal system before it is combusted in the gas turbine, and the sulfur components, particularly SO2, in the exhaust gas of the gas turbine are removed by the desulfurization system.
Similarly, in the IGCC plant disclosed in Japanese Patent No. 2954972, the sulfur components in the exhaust gas of the gas turbine are also removed in the desulfurization system.
However, in the IGCC plants disclosed in Japanese Patent Nos. 2733188 and 2954972, SO3 and dust primarily composed of ammonium sulfate cannot be removed, and as a result, there has been a problem in that the sulfur components and the dust have not been sufficiently removed.